From plankton to top predators: bottom-up control of a marine food web across four trophic levels

1. Abundant mid-trophic pelagic fish often play a central role in marine ecosystems, both as links between zooplankton and top predators and as important fishery targets. In the North Sea, the lesser sandeel occupies this position, being the main prey of many bird, mammal and fish predators and the target of a major industrial fishery. However, since 2003, sandeel landings have decreased by > 50%, and many sandeel-dependent seabirds experienced breeding failures in 2004. 2. Despite the major economic implications, current understanding of the regulation of key constituents of this ecosystem is poor. Sandeel abundance may be regulated 'bottom-up' by food abundance, often thought to be under climatic control, or 'top-down' by natural or fishery predation. We tested predictions from these two hypotheses by combining unique long-term data sets (1973–2003) on seabird breeding productivity from the Isle of May, SE Scotland, and plankton and fish larvae from the Continuous Plankton Recorder survey. We also tested whether seabird breeding productivity was more tightly linked to sandeel biomass or quality (size) of individual fish. 3. The biomass of larval sandeels increased two- to threefold over the study period and was positively associated with proxies of the abundance of their plankton prey. Breeding productivity of four seabirds bringing multiple prey items to their offspring was positively related to sandeel larval biomass with a 1-year lag, indicating dependence on 1-year-old fish, but in one species bringing individual fish it was strongly associated with the size of adult sandeels. 4. These links are consistent with bottom-up ecosystem regulation and, with evidence from previous studies, indicate how climate-driven changes in plankton communities can affect top predators and potentially human fisheries through the dynamics of key mid-trophic fish. However, the failing recruitment to adult sandeel stocks and the exceptionally low seabird breeding productivity in 2004 were not associated with low sandeel larval biomass in 2003, so other mechanisms (e.g. predation, lack of suitable food after metamorphosis) must have been important in this case. Understanding ecosystem regulation is extremely important for predicting the fate of keystone species, such as sandeels, and their predators.

Bridging top down and bottom up: Modelling community preferences for a dispersed rural settlement pattern

This paper explores the scope to bridge top-down and bottom-up perspectives on spatial planning by drawing on EU-funded action research in relation to rural settlement planning in Northern Ireland. The empirical work is located within a review of planning theory that exposes a long running tension between the technocratic stances of government planners and the aspirations of engaged citizens. It demonstrates the operation of a large group planning methodology that delivers community preference with environmental responsibility as a participatory input into planning policy formulation. Transferable insights into the dynamics of spatial planning are identified.

Directed self-assembly of nanorod networks: bringing the top down to the bottom up

Self-assembled electrodeposited nanorod materials have been shown to offer an exciting landscape for a wide array of research ranging from nanophotonics through to biosening and magnetics. However, until now, the scope for site-specific preparation of the nanorods on wafers is limited to local area definition. Further there is little or no lateral control of nanorod height. In this work we present a scalable method for controlling the growth of the nanorods in the vertical direction as well as their lateral position. A focused ion beam (FIB) pre-patterns the Au cathode layer prior to the creation of the Anodized Aluminium Oxide (AAO) template on top. When the pre-patterning is of the same dimension to the pore spacing of the AAO template, lines of single nanorods are successfully grown. Further, for sub-200 nm wide features a relationship between the nanorod height and distance from non-patterned cathode can be seen to follow a quadratic growth rate obeying Faradays law of electrodeposition. This facilitates lateral control of nanorod height combined with localised growth of the nanorods.

What happens in the first 200 ms of word reading : ERP studies on visual word recognition with top-down and bottom-up approaches /

In this thesis, three main questions were addressed using event-related potentials (ERPs): (1) the timing of lexical semantic access, (2) the influence of "top-down" processes on visual word processing, and (3) the influence of "bottom-up" factors on visual word processing. The timing of lexical semantic access was investigated in two studies using different designs. In Study 1,14 participants completed two tasks: a standard lexical decision (LD) task which required a word/nonword decision to each target stimulus, and a semantically primed version (LS) of it using the same category of words (e.g., animal) within each block following which participants made a category judgment. In Study 2, another 12 participants performed a standard semantic priming task, where target stimulus words (e.g., nurse) could be either semantically related or unrelated to their primes (e.g., doctor, tree) but the order of presentation was randomized. We found evidence in both ERP studies that lexical semantic access might occur early within the first 200 ms (at about 170 ms for Study 1 and at about 160 ms for Study 2). Our results were consistent with more recent ERP and eye-tracking studies and are in contrast with the traditional research focus on the N400 component. "Top-down" processes, such as a person's expectation and strategic decisions, were possible in Study 1 because of the blocked design, but they were not for Study 2 with a randomized design. Comparing results from two studies, we found that visual word processing could be affected by a person's expectation and the effect occurred early at a sensory/perceptual stage: a semantic task effect in the PI component at about 100 ms in the ERP was found in Study 1 , but not in Study 2. Furthermore, we found that such "top-down" influence on visual word processing might be mediated through separate mechanisms depending on whether the stimulus was a word or a nonword. "Bottom-up" factors involve inherent characteristics of particular words, such as bigram frequency (the total frequency of two-letter combinations of a word), word frequency (the frequency of the written form of a word), and neighborhood density (the number of words that can be generated by changing one letter of an original word or nonword). A bigram frequency effect was found when comparing the results from Studies 1 and 2, but it was examined more closely in Study 3. Fourteen participants performed a similar standard lexical decision task but the words and nonwords were selected systematically to provide a greater range in the aforementioned factors. As a result, a total of 18 word conditions were created with 18 nonword conditions matched on neighborhood density and neighborhood frequency. Using multiple regression analyses, we foimd that the PI amplitude was significantly related to bigram frequency for both words and nonwords, consistent with results from Studies 1 and 2. In addition, word frequency and neighborhood frequency were also able to influence the PI amplitude separately for words and for nonwords and there appeared to be a spatial dissociation between the two effects: for words, the word frequency effect in PI was found at the left electrode site; for nonwords, the neighborhood frequency effect in PI was fovind at the right elecfrode site. The implications of otir findings are discussed.

Integrating top down policies and bottom up practices in Urban and Periurban Agriculture: an Italian dilemma

The paper deals with some relevant and contradictory aspects of urban and peri-urban agriculture in Italy: the traditional exclusion of agricultural areas from the goals of territorial planning; the separation between top-down policies and bottom-up practices; the lack of agricultural policies at local scale. In the first part the paper summarises the weak relation between urban planning and agriculture, showing how in Italy this gap has been only partially overcome by new laws and plans. Moreover the paper focuses on how, due to the lack of suitable solutions coming from regional and local planning, a large number of vibrant initiatives were started by local stakeholders. In order to show the limitations and the potentialities of these various approaches, three peculiar experiences based on Milan, Turin and Pisa are presented. They give a cross-section of the variegated Italian situation, demonstrating that a major challenge in Italian context affects the fields of governance and inclusiveness.

Top-down and bottom-up approaches to motor skill assessment of children : are child-report and parent-report perceptions predictive of children's performance-based assessment results?

Background/ Aim: Therapists use different types of tests, scales, and instruments to assess children's motor skills, including those classified as being top-down and bottom-up. The aim of the study was to investigate the ability of measures of children's motor skill performance from the perspectives of children and parents (a type of top-down assessment) to predict children's performance-based motor ability test results (a type of bottom-up assessment).
Methods: A convenience sample of 38 children and parents was recruited from Victoria, Australia. Motor skill performance was evaluated from a top-down perspective using the Physical Self-Description Questionnaire (PSDQ) and the Movement Assessment Battery for Children – Second Edition (MABC-2) Checklist to measure children's and parents' perspectives respectively. Motor skill performance was also evaluated from a bottom-up approach using the Bruininks-Oseretsky Test of Motor Proficiency – Second Edition (BOT-2). Data were analyzed using multiple linear regression analysis to determine whether the PSDQ or MABC-2 Checklist was predictive of the children's BOT-2 performance results.
Results: Two predictive relationships were identified based on parents' perspectives, where the total score of the MABC-2 Checklist was found to be a significant predictor of the BOT-2 Manual Coordination motor composite score, accounting for 8.35% of its variance, and the BOT-2 Strength and Agility motor composite score, accounting for 11.6% of its variance. No predictive relationships were identified between the children's self-report PSDQ perspectives and the BOT-2 performance scores.
Conclusions: Therapists are encouraged to utilize a combination of top-down and bottom-up approaches and purposefully to seek parents' and children's perspectives when evaluating children's motor skill performance.

Estimating the relative roles of top-down and bottom-up forces on insect herbivore populations: A classic study revisited

Although most ecologists agree that both top-down and bottom-up forces (predation and resource limitation, respectively) act in concert to influence populations of herbivores, it has proven difficult to estimate the relative contributions of such forces in terrestrial systems. Using a combination of time–series analysis of population counts recorded over 16 years and experimental data, we present the first estimates of the relative roles of top-down and bottom-up forces on the population dynamics of two terrestrial insect herbivores on the English oak (Quercus robur). Data suggest that temporal variation in winter moth, Operophtera brumata, density is dominated by time-lagged effects of pupal predators. By comparison, spatial variation in O. brumata density is dominated by host–plant quality. Overall, top-down forces explain 34.2% of population variance, bottom-up forces explain 17.2% of population variance, and 48.6% remains unexplained. In contrast, populations of the green oak tortrix, Tortrix viridana, appear dominated by bottom-up forces. Resource limitation, expressed as intraspecific competition among larvae for oak leaves, explains 29.4% of population variance. Host quality effects explain an additional 5.7% of population variance. We detected no major top-down effects on T. viridana populations. An unknown factor causing a linear decline in T. viridana populations over the 16-year study period accounts for most of the remaining unexplained variance. We discuss the observed differences between the insect species and the utility of time–series analysis as a tool in assessing the relative importance of top-down and bottom-up forces on herbivore populations.

Bottom up strategies for the morphology control of BaTiO3 particulates

As propriedades funcionais dos materiais ferroeléctricos tais como a polarização reversível, piroelectricidade, piezoelectricidade, elevada actividade óptica não linear e comportamento dieléctrico não linear são fundamentais para a sua aplicação em sensores, microactuadores, detectores de infravermelhos, filtros de fase de microondas e memórias não-voláteis. Nos últimos anos, motivado pelas necessidades industriais de redução do tamanho dos dispositivos microelectrónicos, aumentando a eficiência volumétrica, tem sido feito um grande esforço ao nível da investigação para desenvolver estruturas ferroeléctricas à escala micro- e nano- métrica. É sabido que a redução de tamanho em materiais ferroeléctricos afecta significamente as suas propriedades. Neste sentido e considerando que foi previsto teoreticamente por cálculos ab initio que estruturas do tipo nanocilindros e nanodiscos apresentariam um novo tipo de ordem ferroeléctrica e, na expectativa de alcançar conhecimento para o desenvolvimento de uma nova geração de dispositivos microelectróncos, existe um grande interesse em desenvolver métodos de fabrico de nanoestruturas ferroeléctricas unidimensionais (1D) tais como nanocilindros e nanotubos. As estratégias de fabrico de nanoestruturas 1D até agora descritas na literatura indicam claramente as dificuldades inerentes à sua preparação. Existem duas grandes vias de síntese destas nanoestruturas: i) o método “topdown” que consiste na redução de tamanho de um dado material até à obtenção duma estrutura 1D; e ii) o método “bottom-up” em que átomos, iões e moléculas são agrupados para formar um material 1D. O método “top down” envolve em geral técnicas de desgaste, como o uso do feixe de electrões, que apesar de permitirem elevada precisão no posicionamento e no controlo do tamanho, falham em termos de resolução, exigem muito tempo e causam facilmente defeitos que deterioram as propriedades físicas destes materiais. Na metodologia “bottom up” a utilização de moléculas ou estruturas “molde” tem sido a mais explorada. As estructuras 1D podem também ser preparadas sem recorrer a “moldes”. Neste caso a agregação orientada é promovida pelo recurso a aditivos que controlam o crescimento dos cristais em direcções preferenciais. Neste contexto, neste trabalho utilizaram-se duas estratégias “bottom up” de baixo custo para a preparação de nanopartículas de titanato de bário (BaTiO3) com morfologia controlada: 1) síntese química (em solução e em fase vapor) com utilização de nanotubos de titanato TiNTs) como “moldes” e precursores de titânio 2) síntese química em solução com presença de aditivos. Os nanotubos de titanato de sódio foram preparados por síntese hidrotermal. Como existiam muitas dúvidas acerca da natureza estrutural e do mecanismo de formação dos NTs, a parte inicial do trabalho foi dedicada à realização de um estudo sistemático dos parâmetros intervenientes na síntese e à caracterização da sua estrutura e microestrutura. Foi demonstrado que os NTs têm a fórmula geral A2Ti2O5 (A = H+ or Na+), e não TiO2 (anátase) com defendido por vários autores na literatura, e podem ser preparados por método hidrotermal em meio fortemente alcalino usando como fonte de titânio TiO2 comercial na forma de anátase ou rútilo. A menor reactividade do rútilo exige temperaturas de síntese superiores ou tempos de reacção mais longos. A forma tubular resulta do tratamento hidrotermal e não de processos de lavagem e neutralização subsequentes. Se os NTs forem tratados após a síntese hidrotérmica em água a 200 ºC, transformam-se em nanocilindros. Uma das partes principais desta tese consistiu na investigação do papel dos NTs de titanato no crescimento anisotrópico de BaTiO3. O potencial funcionamento dos NTs como “moldes” para além de precursores foi testado em reacção com hidróxido de bário em síntese em solução e por reacção com um precursor orgânico de bário em fase vapor. Tendo por base os estudos cinéticos realizados, bem como as alterações estruturais e morfológicas das amostras, é possível concluir que a formação do BaTiO3 a partir de NTs de titanato de sódio, ocorre por dois mecanismos dependendo da temperatura e tempo de reacção. Assim, a baixa temperatura e curto tempo de reacção verifica-se que se formam partículas dendríticas de BaTiO3 cuja superfície é bastante irregular (“wild”) e que apresentam estrutura pseudo-cúbica. Estas partículas formam-se por reacção topotáctica na fronteira dos nanotubos de titanato de sódio. A temperaturas mais altas e/ou reacções mais longas, a reacção é controlada por um mecanismo de dissolução e precipitação com formação de dendrites de BaTiO3 tetragonais com superfície mais regular (“seaweed”). A microscopia de força piezoeléctrica mostrou que as dendrites “seaweeds“ possuem actividade piezoeléctrica superior à das dendrites “wild”, o que confirma o papel desempenhado pela estrutura e pela concentração de defeitos na rede na coerência e ordem ferroeléctrica de nanoestruturas. Os nossos resultados confirmam que os NTs de titanato não actuam facilmente como “moldes” na síntese em solução de BaTiO3 já que a velocidade de dissolução dos NTs em condições alcalinas é superior à velocidade de formação do BaTiO3. Assumindo que a velocidade de reacção dos NTs com o precursor de bário é superior em fase vapor, efectuou-se a deposição de um precursor orgânico de bário por deposição química de vapor sobre um filme de NTs de titnato de sódio depositados por deposição electroforética. Estudou-se a estabilidade dos NTs nas diferentes condições do reactor. Quando os NTs são tratados a temperaturas superiores a 700 ºC, ocorre a transformação dos NTs em nanocilindros de anatase por um mecanismo de agregação orientada. Quando se faz a deposição do precursor de bário, seguida de calcinação a 700 ºC em atmosfera oxidante de O2, verifica-se que a superficie dos NTs fica coberta com nanocristais de BaTiO3 independentemente da concentração de bário. O papel dos NTs de titanato no crescimento anisotrópico de BaTiO3 em fase vapor é assim descrito pela primeira vez. Em relação à metodologias de crescimento de partículas na ausência de “moldes” mas com aditivos fez-se um estudo sistemático utilizando 5 aditivos de natureza differente. As diferenças entre aditivos foram sistematizadas tendo em conta as diferenças estruturais e morfológicas verificadas. Está provado que os aditivos podem funcionar como modificadores de crescimento cristalino por alteração do seu padrão de crescimento ou por alteração da cinética de crescimento das faces cristalográficas do cristal. Entre os aditivos testados verificou-se que o ácido poliacrilíco adsorve em faces específicas do BaTiO3 alterando a cinética de crescimento e induzindo a agregação orientada das partículas. O polivinilpirrolidona, o docecilsulfato de sódio e hidroxipropilmetilcelulose actuam mais como inibidores de crescimento do que como modificadores do tipo de crescimento. A D-frutose aumenta a energia de activação da etapa de nucleação não ocorrendo formação de BaTiO3 para as mesmas condições dos outros aditivos. Esta tese clarifica o papel dos NTs de titanato de sódio enquanto precursores e “moldes” no crescimento anisotrópico de BaTiO3 em solução e em fase vapor. É feita também a abordagem do controlo morfológico do BaTiO3 através do uso de aditivos. As estratégias de preparação de BaTiO3 propostas são de baixo custo, reprodutíveis e fáceis de efectuar. Os resultados contribuem para uma melhor compreensão da relação tamanho – morfologia – propriedade em materiais ferroeléctricos nanométricos com vista à sua potencial aplicação.

Top-down or bottom-up: the real choice for public services

This article considers two contrasting approaches to reforming public services in order to meet the needs of people living in poverty. The first approach is top-down, involves categorising individuals (as 'hard to help', 'at risk', etc) and invokes scientific backing for justification. The second approach is bottom-up, emancipatory, relates to people as individuals and treats people who have experience of poverty and social exclusion as experts. The article examines each approach through providing brief examples in the fields of unemployment and parenting policy - two fields that have been central to theories of 'cycles of deprivation'. It is suggested here that the two approaches differ in terms of their scale, type of user involvement and type of evidence that is used for their legitimation. While the article suggests that direct comparison between the two approaches is difficult, it highlights the prevalence of top-down approaches towards services for people living in poverty, despite increasing support for bottom-up approaches in other policy areas.

An overview of top-down vs. bottom-up models for informal settlement upgrading in South Africa

The paper explores informal settlement upgrading approaches in South Africa and presents a review of top-down vs. bottom-up models, using experience and lessons learned from the Durban metropolitan area. Reflections on past upgrading efforts suggest that top-down policies in South Africa have not been successful to date. By contrast, participatory techniques, such as planning activism, can be used to enhance community empowerment and a sense of local ownership. This paper reveals that although the notion of ‘bottom-up’, participatory methods for community improvement is often discussed in international development discourses, the tools, processes and new knowledge needed to ensure a successful upgrade are under-utilised. Participation and collaboration can mean various things for informal housing upgrading and often the involvement of local communities is limited to providing feedback in already agreed development decisions from local authorities and construction companies. The paper concludes by suggesting directions for ‘co-producing’ knowledge with communities through participatory, action-research methods and integrating these insights into upgrading mechanisms and policies for housing and infrastructure provision. The cumulative impacts emerging from these approaches could aggregate into local, regional, and national environmental, social and economic benefits able to successfully transform urban areas and ensure self-reliance for local populations.

Top-predator control-induced trophic cascades: an alternative hypothesis to the conclusion of Colman et al.

Recently argued that observed positive relationships between dingoes and small mammals were a result of top-down processes whereby lethal dingo control reduced dingoes and increased mesopredators and herbivores, which then suppressed small mammals. Here, I show that the prerequisite negative effects of dingo control on dingoes were not shown, and that the same positive relationships observed may simply represent well-known bottom-up processes whereby more generalist predators are found in places with more of their preferred prey. Identification of top-predator controlinduced trophic cascades first requires demonstration of some actual effect of control on predators, typically possible only through manipulative experiments with the ability to identify cause and effect.

The roles of feature-specific task set and bottom-up salience in attentional capture: An ERP study

We investigated the roles of top-down task set and bottom-up stimulus salience for feature-specific attentional capture. Spatially nonpredictive cues preceded search arrays that included a color-defined target. For target-color singleton cues, behavioral spatial cueing effects were accompanied by cueinduced N2pc components, indicative of attentional capture. These effects were only minimally attenuated for nonsingleton target-color cues, underlining the dominance of top-down task set over salience in attentional capture. Nontarget-color singleton cues triggered no N2pc, but instead an anterior N2 component indicative of top-down inhibition. In Experiment 2, inverted behavioral cueing effects of these cues were accompanied by a delayed N2pc to targets at cued locations, suggesting that perceptually salient but task-irrelevant visual events trigger location-specific inhibition mechanisms that can delay subsequent target selection.